1. Field of the Invention
The present invention relates generally to chemical mechanical polishing (CMP) Em systems and techniques for improving the performance and effectiveness of CMP operations. Specifically, the present invention relates to the CUM systems that utilize a web-style conditioner for conditioning pad surfaces.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform CMP operations, including polishing, buffing and wafer cleaning. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. At each metallization level and/or associated dielectric layer, there is a need to planarize the metal and/or dielectric material. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove excess metallization.
CMP systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to polish, buff, and scrub one or both sides of a wafer. Slurry is used to facilitate and enhance the CMP operation. Slurry is most usually introduced onto a moving preparation surface, e.g., belt, pad, brush, and the like, and distributed over the preparation surface as well as the surface of the semiconductor wafer being buffed, polished, or otherwise prepared by the CMP process. The distribution is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the friction created between the semiconductor wafer and the preparation surface.
FIG. 1 illustrates an exemplary prior art CMP system 100. The CMP system 100 of FIG. 1 is a belt-type system, so designated because the preparation surface is an endless polishing pad 108 mounted on two drums 114 which drive the polishing pad 108 in a rotational motion as indicated by polishing pad rotation directional arrows 116. A wafer 102 is mounted on a carrier 104. The carrier 104 is rotated in direction 106. The rotating wafer 102 is then applied against the rotating polishing pad 108. Some CMP processes require significant force F to be applied. A platen 112 is provided to stabilize the polishing pad 108 and to provide a solid surface onto which to apply the wafer 102. Slurry 118 including of typically an aqueous solution containing dispersed abrasive particles (e.g., SiO2, Al2O3, CeO2, etc.) is introduced upstream of the wafer 102. The process of scrubbing, buffing and polishing of the surface of the wafer could be achieved by using either a non-fixed abrasive polishing pad or a fixed abrasive polishing pad. Due to having different characteristics, the conditioning of the non-fixed abrasive polishing pads are to some extent different than that of the fixed abrasive polishing pads. Below are brief descriptions of the conditioning of non-fixed abrasive polishing pads as well as fixed abrasive polishing pads.
The non-fixed abrasive polishing pads are composed of porous or fibrous materials and fixed abrasive particles, which are introduced into the system in the form of an aqueous solution (also known as slurry). As illustrated in FIG. 1, after the non-fixed abrasive polishing pad 108 polishes the wafer 102, the conditioner disk 122 of the conditioning assembly 110 is applied to the surface of the non-fixed abrasive polishing pad 108 thus removing the residue, consisting of abrasive particles of the slurry and the particulates removed from the wafer 102 (which clog the porous 61 surface of the pad 108). As illustrated in the cross-sectional view of a conditioning assembly 110 of FIG. 1A-1, the surface of a conditioner disk 122 includes a diamond array 124. The non-fixed abrasive polishing pad 108 is conditioned as the conditioner disk 122 and thus the diamond array 124 are moved along a track bar 123 and across the polishing surface of the non-fixed abrasive polishing pad 108. Accordingly, in non-fixed abrasive polishing pad CMP systems, the conditioner disk 122 removes the particulate materials and the attached slurry materials from the surface of the non-fixed abrasive polishing pad 108 thereby cleaning and roughening the non-fixed abrasive polishing pad 108 as well as exposing a fresh layer of the non-fixed abrasive polishing pad.
Ordinarily, different sizes of conditioning disks can be used to condition the surface of the non-fixed abrasive polishing pad 108. Furthermore, as some non-fixed abrasive polishing pads require conditioning by extra fine abrasive particles, the conditioning disks may have abrasive particles having various sizes. One example of abrasive particles is defined as diamond arrays, which may be mounted on the carrier disks utilizing different bonding technologies. However, one common problem in utilizing diamond arrays for conditioning the non-fixed abrasive polishing pads is the dislodgment of diamonds of a diamond arrays. As illustrated in FIG. 1A-2, the dislodgment of diamonds 124xe2x80x2 of a diamond array 124 occurs as a result of the extensive wear of the conditioning disk 122. Furthermore, the dislodgment of the diamonds 124xe2x80x2 occur irrespective of the size of the carrier disks 122 and the dimensions of the diamonds 124xe2x80x2 of the diamond arrays 124 and the technology implemented to mount the diamond arrays 124 on the conditioner disks 122. The dislodged diamonds 124xe2x80x2 could remain on the polishing pad 108, could be caught between polishing pad 108 and the wafer 102 during the polishing cycle, and could scratch the surface of the wafer 102 being polished.
Another challenge in utilizing conditioning disks with diamond arrays is maintaining well-kept diamond arrays having very small diamonds. Even after a short wear time of the conditioning disk, these diamonds easily become loose. Even small diamonds being loose on a pad during polishing could cause severe scratching of the surface of the semiconductor wafer. This could create electrical shorts in the electronic circuit devices, and could make some devices on the wafer inoperable. This severely reduces yield. Therefore, conditioning disks should be often replaced to avoid excessive wear. In either situation, the dislodgment of the diamonds 124xe2x80x2 as well as the extensive wear of the conditioning disk reduce the removal rate of the particulates and the attached slurry. They also increase the overall defects and micro-scratching of wafers during the CMP process. Furthermore, the replacement of the entire conditioner disk is very inconvenient as well as time consuming. Additionally, the CMP system must be taken off-line so as to allow the replacement of the entire conditioner disk or the dislodged diamonds, thereby reducing the throughput of the CMP system.
One particular type of polishing pad, which requires conditioning by extra fine abrasive materials, is a fixed abrasive polishing pad. FIG. 1B-1 depicts a fixed-abrasive polishing pad 108 having a fixed abrasive polishing layer. Embedded and extended through out the surface of this type of polishing pad are several three-dimensional cylindrical protrusions, defined as xe2x80x9cpillarsxe2x80x9d 108xe2x80x2. Each pillar 108xe2x80x2 may have a diameter of approximately about 200 micrometers and an approximate height of about 40 micrometers. The cross-sectional view of the fixed abrasive polishing pad of FIG. 1B-2 reveals that each pillar 108xe2x80x2 contains a plurality of abrasive particles 108a. Further depicted on the fixed abrasive polishing pad 108 are a plurality of pillar isolation regions 108b.Accordingly, in CMP systems wherein fixed abrasive polishing pad 108 are used, the polishing of the wafer 102 is achieved by the friction between the embedded abrasive particles 108a and the surface of the wafer 102 in the polishing interface.
Furthermore, in some fixed abrasive CMP systems, additional slurry may be introduced into the polishing interface to enhance and expedite the planarization process. As depicted in FIG. 1B-3, each fixed abrasive pillar 108xe2x80x2 consists of a polymer matrix of a desired hardness, and the abrasive particles 108a are embedded (i.e., fixed) within each of the pillars 108xe2x80x2. For the pillar 108xe2x80x2 to perform the polishing work on the semiconductor substrate (i.e., wafer 102), a top layer 111 of the polymer matrix must be removed in order to expose fresh embedded fixed abrasive particles 108a which can then be placed in contact with the surface of wafer 102. Consequently, the fixed abrasive polishing pad 108 must be conditioned so that the polymer layer 111 is removed from the top of the pillars 108xe2x80x2 so as to expose fresh fixed abrasive particles 108a. Accordingly, the conditioning of fixed abrasive polishing pads is directed toward xe2x80x9cdressingxe2x80x9d the fixed abrasive polishing pads by exposing fresh abrasive particles. The conditioning of the fixed abrasive polishing pad, which is achieved by the removal of the top layer 111 of the polymer matrix of the fixed abrasive polishing pad pillars so as to expose fresh fixed abrasive particles, is hereinafter referred to as xe2x80x9cdressing.xe2x80x9d
Currently, the dressing of the fixed abrasive polishing pad 108 is commonly achieved by the motion of the topography features of the wafer 102. As illustrated in FIG. 1B-4, the carrier 104 applies the wafer 102 to the fixed abrasive polishing pad 108. Also depicted in FIG. 1B-4 are the edges of a plurality of topography features 102a. As a consequence of the friction of the fixed abrasive polishing pad 108 and the wafer features 102a,the edges of the topography features 102a come into contact with the top layer 111 of polymer matrix thus removing the top layer 111 of the polymer matrix of the pillars 108xe2x80x2 , thereby exposing fresh abrasive particles 108a. As a result, the dressing of the fixed abrasive polishing pad and thus the chemical mechanical polishing process become wafer topography pattern sensitive. More specifically, the dressing of the fixed abrasive polishing pad 108 becomes dependent upon the relative sizes of the features 102a and the pillars 108a as well as the number of the edges of the features 102a that go across each pillar 108a within a specific length of time. Thus, in situations where the sizes of the wafer features 102a are small, the fixed abrasive polishing pad 108 is conditioned significantly fast. However, in the situations where the width of the wafer feature 102a are larger than approximately 10 microns, the fixed abrasive polishing pad is conditioned at a significantly lower rate. Consequently, the dependency of the removal rate of top layer of polymer matrix of the pillars from the fixed abrasive polishing pads on the feature size and/or density of the wafers can play a significant role in discouraging the use of the fixed abrasive polishing pads to perform chemical mechanical polishing.
A solution would be to decouple the dressing of the fixed abrasive polishing pad from the polishing stage of the chemical mechanical polishing process. In such a situation, the dressing of the fixed abrasive polishing pad may be achieved through the use of an external dressing medium having extra fine abrasive particles resembling the features often found on the surface of wafer to be polished. The fixed abrasive polishing pads have Mylar backings and abrasive particles that are substantially smaller than 1 micron and are preferably around 0.1 micron in diameter. The diamond disks having diamonds that are small enough to perform gentle conditioning work on the aforementioned fixed abrasive pads can be manufactured. However, manufacturing of such diamond dresser disks is not production worthy as the dresser diamond disks wear relatively quickly and thus lose their effectiveness. Therefore, the dresser diamond disks must be replaced after the fixed abrasive polishing pad polishes only a couple of wafers. Furthermore, the dressing diamond disks must be replaced in their entirety with fresh disks thus making it necessary for the CMP system to be taken off-line, thereby reducing throughput. Additionally, the process of replacing them could be very time consuming and labor intensive.
In view of the foregoing, a need therefore exists in the art for a conditioner assembly for use in a chemical mechanical polishing system that will enable conditioning a polishing pad utilized in polishing surface layers of a wafer, wherein the conditioner assembly is less expensive to maintain and is more effectively serviced after the use of the conditioning material degrades the effectiveness of the conditioning operation.
Broadly speaking, the present invention fills these needs by providing an apparatus and related methods for efficiently conditioning a polishing surface of a polishing pad. Preferably, the CMP system is designed to implement a dressing media that is less expensive to maintain and is more efficiently serviced after it loses its effectiveness to condition. In preferred embodiments, the dressing media is connected between a feed-roll and a take-up roll. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a polishing pad conditioner for use in a chemical mechanical polishing (CMP) apparatus is disclosed. Included in the polishing pad conditioner is a web dressing media having a contact surface defined between a first point and a second point. The first point is separate from the second point. The web dressing media is configured to be positioned over a fixed abrasive polishing pad such that the contact surface of the web dressing media is configured to be applied to the abrasive polishing surface of the fixed abrasive polishing pad. The polishing pad conditioner further includes a pressure application plate configured to be applied against an application surface of the web dressing media. In another embodiment, a method for conditioning a polishing pad is disclosed. The method includes providing a fixed abrasive polishing pad having an abrasive polishing surface. The fixed abrasive polishing pad is configured to move between a first point and a second point that is separate from the first point. Further included in the method is providing a web dressing media between the first point and the second point. A contact surface of the web dressing media is defined above an abrasive polishing surface of the fixed abrasive polishing pad. Also included in the method is dressing the abrasive polishing surface of the fixed abrasive polishing pad by applying the contact surface of the web dressing media to the abrasive polishing surface of the fixed abrasive polishing pad.
In still a further embodiment, a system for conditioning a pad is disclosed. The system includes a pad conditioning media, a feed-roll containing a supply of the pad conditioning media, and a take-up roll for receiving an end of the pad conditioning media. Also included in the system is a pressure application member defined between the feed-roll and the take-up roll. The pressure application member is designed to apply pressure onto the pad conditioning media as the pad conditioning media is applied against the pad to cause a conditioning of a surface of the pad.
The advantages of the present invention are numerous. Most notably, instead of disk-style or linear pad conditioners, a supply of conditioning media is provided between a feed-roll and a take-up roll in a web handling arrangement. Thus, replacing used portions of the conditioning media with fresh portions of the conditioning media can be accomplished utilizing minimal effort and in significantly less amount of time. Furthermore, the re-supplying of the conditioning media can be achieved easily and expeditiously thereby minimizing the length of time needed to take the chemical mechanical polishing system off-line thus having minimal effect on the system""s throughput. Moreover, the programmable indexing feature of the apparatus and the methods of the present invention provides a consistent pad conditioning over time, further eliminates the instability of the conditioning material wear associated with the prior art, improves overall defects, and increases the overall pad life. In addition, the present invention improves the overall micro scratching and defects of the CMP process. Particularly, the apparatus and the methods of the present invention provide for a substantially uniform dressing rate in embodiments wherein substantially fine abrasive conditioning of the polishing surface layers of a polishing pad is desired irrespective of the wafer topography feature density or the wafer topography feature sizes. Most importantly, the embodiments of present invention are very beneficial in the implementation of fixed abrasive technology.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.